Collection(Set), Using a HashSet

[Arjun Reddy]

Hi Guys,

In the following code, How come each time I print the set, am getting a sorted result?

 
 
package collections;
 
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
 
public class SetTest {
 

public static void main(String[] args) {


Set s1 = new HashSet();
s1.add("c");
s1.add("a");
s1.add("b");
System.out.println("Printing the set");
System.out.println(s1);


HashSet s2 = new HashSet();
s2.add("c");
s2.add("a");
s2.add("b");
System.out.println(s2);

}
 
}
   

Thanks.

[Henry Wong]

In the following code, How come each time I print the set, am getting a sorted result?

Really? When I run this code, my ordering is not sorted.... I get A, C, B.

And BTW, even if it was A, B, C, can it be attributed to dumb luck? Three values is certainly not enough to prove that the results is always sorted.

Henry
[ July 25, 2008: Message edited by: Henry Wong ]

[Arjun Reddy]

Um.. yeah but how come your getting A,C,B. Shouldn't you be getting C,A,B, the order which they were inserted?

Thanks.

[burak cetin]

Hashset is neither ordered nor sorted. so when you access the variables the outcome is unpredictable. there was a good explanation of the difference between ordered and sorted in kate&bert.

BC
[ July 25, 2008: Message edited by: burak cetin ]

[Arjun Reddy]

Um.. sorted means 1,2,3,4 etc.. or a,b,c,d etc.. whats ordered?

Thanks.

[Chandra Bhatt]

Originally posted by Arjun Reddy:
Um.. sorted means 1,2,3,4 etc.. or a,b,c,d etc.. whats ordered?

Thanks.

Ordered means in what order like (First In First Out) or (Last In First Out) or any other way of inserting and retrieving from the Collection. But Set is not ordered, means it does not have any order of the above avtivities. If you get so called sorted output (a,b,c) its just a chance that for you it was like that (to confuse you more)

[Deepak Bajoria]

I think it all depends on the hash function used by the JVM. Like for e.g if a hashCode() simply returns the ascii value of the letter, the output would be sorted

[Henry Wong]

Originally posted by Deepak Bajoria:
I think it all depends on the hash function used by the JVM. Like for e.g if a hashCode() simply returns the ascii value of the letter, the output would be sorted

Not really. First, it depends on how the buckets are implemented. The Set may not map linearly with hashcode. Second, there may not be a one to one mapping between buckets and hashcodes. Two different letter may end up in the same bucket, then it will depend on how each bucket is implemented.

Henry

[Henry Wong]

One other point, if something is not sorted or ordered, it doesn't mean that the ordering random. Don't expect iterations through the Set to yield different results -- it may, but it may not. The point is, any ordering is purely coincidental, and the HashSet collection has not been implemented with any ordering.

Henry

[Arjun Reddy]

Thank you guys.